The present disclosure relates to a technique for receiving an electric power from a primary coil via magnetic coupling and supplying the electric power to a load.
An electric power receiving device of various types has been proposed that includes a secondary-side coil (secondary coil) provided so as to face a primary-side induction line (primary coil) and is configured to generate an induced voltage in the secondary coil by a high-frequency current flowing through the primary coil and to generate an electric power for driving a load based on the generated induced voltage.
An example of an electric power receiving circuit disclosed in Japanese Unexamined Patent Application Publication No. H10-108390 is configured to rectify an output of a resonance circuit formed of a secondary-side coil and a capacitor connected in parallel to each other, to convert the rectified voltage into an output voltage having a specified voltage value, and to output the output voltage to a load. In this electric power receiving circuit, a resonance frequency of the resonance circuit is matched to a frequency of a high-frequency current flowing through a primary-side induction line, and an electric power can thereby be received efficiently from the induction line.
However, a value of inductance in the secondary coil and a value of capacitance in the capacitor actually have variations depending on characteristics of elements. Furthermore, the value of inductance in the secondary coil is also changed due to temperature of the secondary coil, energizing current, secular changes, and so on. Thus, in the above-described electric power receiving circuit, it is not easy, actually, to resonate the secondary-side resonance circuit at a frequency of an alternating current flowing through the primary-side induction line.
On the other hand, in an example of an electric power receiving device disclosed in Japanese Unexamined Patent Application Publication No. 2012-143135, such a problem that the resonance point is not fixed due to various factors, such as variations in characteristics of elements, and so on, is solved as follows. Specifically, this electric power receiving device includes an electric power receiving section having a series resonance circuit configured with a secondary coil and a resonance capacitor, and is configured to convert an electric power inputted from the electric power receiving section into a direct current by means of a converter and to supply the direct current to a load. It is preferred that the series resonance circuit is fully resonant at a frequency of an alternating current on the primary coil side (i.e., it is preferred that a combined reactance becomes zero at the frequency); however, it is often the case, actually, that the resonance point is not fixed due to various factors, such as variations in characteristics of elements, and so on, and that a voltage (reactance voltage) is generated in the series resonance circuit.
Thus, in this electric power receiving device, a reducing-voltage for reducing the reactance voltage generated in the electric power receiving section is generated by the converter, and the reducing-voltage is applied to the electric power receiving section. An actual input current inputted from the electric power receiving section is detected, and the reducing-voltage is calculated using the detected input current and an impedance (including the combined reactance in the series resonance circuit) in the electric power receiving section. According to this technique, the reducing-voltage corresponding to the actual input current is calculated and applied to the electric power receiving section, and thus, in the electric power receiving device as a whole, inhibition of occurrence of resonance by the reactance voltage in the electric power receiving section can be reduced.